Systems for the recycling of exhaust gas in motor vehicles are known from the prior art. These systems reduce the nitrogen oxides in the exhaust gases, in particular in the exhaust gases of motor vehicles operated with diesel fuel, and reduce fuel consumption of motor vehicles operated with gasoline. In generic systems of the recycling of exhaust gas, fresh air to the internal combustion engine is mixed with cooled or non-cooled exhaust gas in order to meet the legal guidelines of the regulations for exhaust gas/emission regarding the nitrogen oxides, but also for the emission hydrocarbons, particles and/or carbon dioxide. In the generic systems, exhaust gas is removed from the exhaust-gas stretch outside of the engine and is supplied via the mixing with fresh air to a new combustion.
During combustion under high temperatures polluting nitrogen oxides are produced, in particular when lean mixtures are used, that is, in the partial load range in the internal combustion engine of motor vehicles. In order to reduce the emission of nitrogen oxides, a lowering of the high temperature peaks and a reduction of the excess air during the combustion are necessary. Due to the lower concentration of oxygen in the fuel-air mixture, the speed of the combustion process and the maximal combustion temperatures are reduced. Both effects are achieved by mixing in a partial mass flow of the exhaust gas to the fresh air current taken in by the internal combustion engine.
In the case of motor vehicles operated with diesel fuel, a system for recycling exhaust gas also brings about the reduction of the emission of noise in addition to reducing the amount of oxygen and the temperature peaks during the combustion. In addition, in the case of motor vehicles operated with gasoline with a system for recycling exhaust gas, throttle losses are also reduced.
However, the mixing in of the recycled current of exhaust gas with high temperatures reduces the cooling effect and also the degree of efficiency of the internal combustion engine. In order to counteract these reductions the exhaust gas is cooled off prior to the admixture in a heat exchanger, referred to as an exhaust gas heat exchanger or exhaust gas recycling cooler. In the case of motor vehicles operated with gasoline the additional cooling of the exhaust gas brings about an increase of the compression ratio of the air supplied to the internal combustion engine.
Laws regarding the standards for exhaust gases and requirements for fuel consumption in motor vehicles are becoming increasingly strict, bringing about an increased cooling requirement. Additionally, space for the components in the motor vehicle is becoming smaller and smaller.
Systems for the recycling of exhaust gas with different types of exhaust gas heat exchangers are known from the prior art. In one embodiment, the exhaust gas to be cooled and a coolant, preferably the cooling liquid of the cooling circuit of the internal combustion engine and therefore two media, flow through the traditional exhaust gas heat exchanger. The exhaust gas is conducted in tubes or conduits with different shapes through the exhaust gas heat exchanger. The coolant flows around the tubes or conduits on their outside so that the mass flow of the coolant flows in an intermediate space formed by a housing and the tubes or conduits. The housing surrounds the tubes or conduits and the intermediate space. A distinction is made, between exhaust gas heat exchangers with an I flowthrough, a U flowthrough, or an S flowthrough as a function of the number of the reversals of the direction of flow of the exhaust gas current and of the associated shape of the tubes or conduits.
The structural components conducting the exhaust gas are preferably made of high-grade steel in order to achieve a high resistance to temperature and to corrosion. High-grade steel, aluminum or plastic are used for the housing in contact with the coolant and the environment, depending on the design of the exhaust gas heat exchanger.
Systems for the recycling of exhaust gas that are known from the prior art, and in addition to the exhaust gas heat exchanger, comprise a valve and a bypass for the recycling of non-cooled exhaust gas. The bypass is opened at special operating points of the internal combustion engine, for example, during a cold start, in order to avoid the formation of condensate in the exhaust gas heat exchanger.
In order to conduct exhaust gas from the exhaust gas side to the suction side of the internal combustion engine, a necessary pressure gradient from the exhaust gas side to the suction side is needed. In certain arrangements for removing a part of the exhaust gas or for feeding the exhaust gas into the fresh air on the intake side, or in certain operating modes of the internal combustion engine, the pressure gradient is not sufficient for transferring the mass flow of the exhaust gas, which is the case, in particular, in the design of the system for the recycling of exhaust gas at low pressure. The recycling of exhaust gas at low pressure is after a turbocharger on the exhaust gas side and in front of a turbocharger on the suction side. In addition, in the case of a slight pressure gradient, a reliable dosing of the exhaust gas to be mixed with fresh air can be ensured only with difficulty. In order to ensure the pressure gradient between the exhaust gas side and the suction side of the internal combustion engine, and to ensure mass flow of the exhaust gas, additional compressors for compressing the mass flow of the exhaust gas are used.
DE 10 2008 018 583 A1 discloses an exhaust gas recycling system for an internal combustion engine with an exhaust gas recycling valve arranged in an exhaust gas recycling line. A first exhaust gas cooler is arranged in the exhaust gas recycling line and a turbocooling unit is arranged in the direction of flow of the exhaust gas behind the first exhaust gas cooler in the exhaust gas recycling line. The turbocooling unit is constructed to be circumventable by a bypass conduit and comprises a compressor, a second exhaust gas cooler, and a turbine mechanically coupled to the compressor. The compressor is driven by the power given off by the turbine.
US 2010/0293943 A1 teaches a power plant with an internal combustion engine, in particular a diesel engine, exhaust gas heat exchangers, and a compressor driven by an exhaust gas turbine for making the charging air available. The exhaust gas turbine and the compressor are directly coupled mechanically.
As is known, even electrically driven compressors, in particular radial compressors, are used for making the pressure gradient available between the exhaust gas side and the suction side of the internal combustion engine for transporting the certain mass flow of the exhaust gas. The electrically driven radial compressor comprises a compressor wheel connected by a shaft or a transmission to an electrical motor. The compressor wheel is surrounded by a compressor housing especially constructed for conducting the flow. On account of the special geometry, the compressor housing is preferably manufactured as a cast part of steel or aluminum.
In systems for recycling exhaust gas with an exhaust gas heat exchanger and a compressor, which are known from the prior art, the components are constructed independently and separate from one another. The separate construction has as a consequence an elevated number of structural components, an elevated space requirement, a high weight, and elevated manufacturing and assembly costs as a consequence. In addition, possible positive thermodynamic and engineering interactions between the exhaust gas heat exchanger and the compressor cannot be utilized.
Accordingly, there exists a need in the art for a device available for the recycling of exhaust gas of an internal combustion engine with which the mass flow of the exhaust gas should be cooled and/or compressed before being recycled to the fresh air taken in by the internal combustion engine. The device should have a simple construction consisting of a minimal number of components with a minimal space requirement and a low weight. In addition, the expenses for the manufacture, service and assembly should be minimal.